1. Field of the Invention
This invention relates to a communication network, in particular a communication network for dynamically allocating channels.
2. Description of the Prior Art
The popularity of cellular communication is, in part, due to its ability to allow a relatively large number of users to establish communication links over a relatively limited bandwidth. However, as the popularity of cellular communication continues to increase, the demands for increased capacity continue.
Time Division Multiple Access (TDMA) cellular communication systems increase capacity by splitting a carrier frequency into a plurality of timeslots, thereby allowing a plurality of communication channels to be established over the same carrier frequency.
To allow speech data to be transmitted in a timeslot, the speech data is compressed using a codec.
To further increase capacity certain TDMA standards, for example GSM, allow the use of a half rate codec. The half rate codec cuts the amount of data needed to adequately represent human speech sounds by half when compared with a full rate codec, thereby allowing two channels to share the same time slot on a carrier with minimal degradation in speech quality.
The GSM standard allows two radiotelephones operating at half speech rate to use the same resource as a single full speech rate radiotelephone by alternatively transmitting the respective radiotelephone signals in the assigned timeslot. Therefore, when system capacity is being stretched, a new channel can be established at half speech rate, with only a minimum deterioration in speech quality. When system capacity requirements are low, new channels can be established at full speech rate.
However, the use of a half speech rate channel has to be determined at channel set-up. As system capacity varies with time this may result in the capacity of the network not being optimally configured at all times.
It would be desirable to improve this situation.